F325 Definitions Flashcards
Acid dissociation constant
For an acid HA,
Ka = [H+][A-]/[HA]
pKa = -log10Ka
Ka = 10^-pKa
Acid - Base Pair
A pair of two species that differ by a proton.
Activation Energy
The minimum energy required to start a reaction by the breaking of bonds.
Alkali
A type of base that dissolves in water to form hydroxide ions (OH- ions).
Average Bond Enthalpy
The average enthalpy change that takes place when breaking, by homolytic fission, 1 mol of a given type of bond in the molecules of a gaseous species.
Boltzmann Distribution
A diagram showing the distribution of energies of the molecules at a particular temperature.
Bond dissociation enthalpy
The enthalpy change that takes place when breaking, by homolytic fission, 1 mol of a given bond in the molecules of a gaseous species.
Brønsted-Lowry Acid
A proton Donor
Brønsted-Lowry Base
A proton Acceptor
Buffer Solution
A solution which minimises the pH change when a small amount of a strong acid or base is added.
Catalyst
A substance that increases the rate of reaction by creating an alternative reaction pathway without being used up in the process.
Complex ion
Transition Metal ion bonded to a number of ligands by dative covalent bonds (also known as coordinate bonding).
Conjugate Acid
A species formed when a proton is added to a base.
Conjugate Base
A species formed when a proton is removed from an acid.
Coordination Number
The total number of coordinate bonds formed between the central metal ion and any ligands.
Displacement Reaction
A reaction in which a more reactive element displaces a less reactive element from an aqueous solution of its ions.
Disproportionation reaction
The oxidation and reduction of the same species in a redox reaction.
Dynamic Equilibrium
The equilibrium that exists in a closed system when the rate of the forwards reaction is equal to the rate of the reverse reaction.
Enthalpy change of atomisation
Enthalpy change when 1 mole of gaseous atoms are formed from the element in its standard state.
Enthalpy change of formation
Enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions.
Enthalpy change of combustion
Enthalpy change when 1 mole of a substance is reacted completely with oxygen under standard conditions, all reactant s and products being in their standard states.
Enthalpy change of hydration
Enthalpy change when 1 mole of gaseous ions is dissolved in water to form 1 mole of aqueous ions, under standard conditions.
Enthalpy change of neutralisation
Energy change when one mole of water is created by the neutralisation of an acid with an alkali under standard conditions.
Enthalpy change of reaction
Enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states.
Enthalpy change of solution
Enthalpy change when 1 mole of a compound dissolves in water. under standard conditions.
Electron shielding
The repulsion between electrons in different inner shells. Shielding reduce the net attractive force from the positive nucleus on the outer shell electrons.
End Point
The point in a titration at which there are equal concentrations of the weak acid and conjugate base forms of the indicator.
Endothermic
Energy transfer from the surroundings.
Exothermic
Energy transfer to the surroundings.
Entropy
Measure of the disorder of a system.
Entropy change of reaction
The entropy change that accompanies a reaction in the molar quantities expressed in the chemical equation under standard conditions, all the reactants and products being in their stander states.
Enthalpy
The heat content that is stored in a chemical system.
Enthalpy cycle
A diagram showing alternative routes between reactants and products that allows the indirect determination of an enthalpy change from other known enthalpy changes using Hess’s law.
Enthalpy profile diagram
A diagram for a reaction to compare the enthalpy of the reactants with the enthalpy of the products.
Equivalence point
The point in a titration at which one solution has reacted equally with a second solution meaning that the molar quantities match the stoichiometry of the reaction that is taking place.
First electron affinity
Enthalpy change when 1 electron is added to each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1- ions.
Second electron affinity
Enthalpy change when 1 electron is added to each ion in 1 mole of gaseous 1- ions to form 1 mole of gaseous 2- ions.
First ionisation energy
Energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.
Second ionisation energy
Energy needed to remove 1 electron from each 1+ ion in 1 mole of gaseous atoms to form 1 mole of gaseous 2+ ions.
Free Energy Change (∆G)
∆H - T∆S It reflects the balance between the enthalpy and entropy changes. It allows us to predict whether a reaction is feasible.
Fuel Cell
An electrochemical cell that uses external fuel and an oxidant to provide electrical energy. It needs both in a constant supply to continue working. At the same time, the waste products are removed.
Half-life
The time it takes for the concentration of a reactant to decrease by half.
Hess’s Law
If a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route.
Heterogeneous catalysis
A reaction in which the catalyst has a different physical state from the reactants; frequently the reactants are gases whilst the catalyst is a solid.
Heterogeneous equilibrium
An equilibrium in which the species making up the reactants and products are in different physical states.
Homogeneous catalysis
A reaction in which the catalyst and reactants have the same physical state which is most frequently the aqueous or gaseous state.
Homogeneous equilibrium
An equilibrium in which the species making up the reactants and products are in the same physical state.
Initial rate of reaction
The change in concentration of a reactant or product per unit time at the start of the reaction t = 0.
Lattice enthalpy
Enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions.
Le Chatelier’s Principle
When a condition affecting a dynamic equilibrium is changed the equilibrium shifts in the direction that opposes the change.
Ligand
Ion or molecule that can donate a pair of electrons to a central metal ion by forming a dative covalent bond (coordinate bond) with it.
Ligand substitution
A reaction where one ligand is replaced by another.
Limiting reagent
A substance in a chemical reaction that runs out first.
Order
The power to which the concentration of the reactant is raised in the rate equation.
Overall order
The sum of the individual orders.
Oxidation
The loss of electron / an increase in oxidation number.
Oxidation number
A measure of the number of electrons that an atom uses to bond with atoms of another element. Oxidation numbers are derived from an set of rules.
Oxidising agent
A reagent that oxidises (takes electrons from) another species.
Periodicity
A regular periodic variation of properties of elements with atomic number and position in the periodic table.
pH
pH = -log10[H+]
Proton exchange membrane (PEM)
A semi permeable membrane that separates the cathode from the anode in a hydrogen fuel cell. Only protons and not electrons can pass through it.
Rate constant k
The constant that links the rate of reaction with the concentrations of the reactants raised to the power of their orders in the rate equation.
Rate of reaction
The rate of change in concentration of a reactant or product over time.
Rate-determining step
The slowest step in the reaction mechanism of a multistep reaction.
Reaction mechanism
A series of steps that, together, make up the overall reaction.
Redox reaction
A reaction in which both reduction and oxidation take place.
Reducing agent
A reagent that reduces (adds electrons to) another species.
Reduction
The gain of electrons / decrease in oxidation number
Specific heat capacity, c
The energy required to raise the temperature of 1g of a substance by 1 degree.
Stability constant, Kstab
The equilibrium constant for an equilibrium existing between a transition metal ion surrounded by water ligands and the complex formed when the same ion has undergone a ligand substitution reaction.
Standard electrode potential (of a half cell)
The emf of a half cell compared with a standard hydrogen half cell, measured at 298 K with solution concentrations of 1 moldm^-3 and a gas pressure of 101 kPa (1 atm).
Storage cell
Sealed system containing all the chemical components necessary for a redox reaction but with physical separation which means that the reaction only proceeds when electrons can travel through an external wire. The free energy released when the cell reaction takes place is used to power an external device.
Strong Acid
An acid that fully dissociates in aqueous solution.
Thermal decomposition
The breaking up of a chemical substance with heat into at least two chemical substances.
Transition element
Element that forms one or more stable ions with a partially filled d sub-shell.
Weak Acid
An acid that partially dissociates in aqueous solution.
